The SphinX X-ray spectrophotometer on the CORONAS-PHOTON spacecraft measured soft X-ray emission in the 1–15 keV energy range during the deep solar minimum of 2009 with a sensitivity much greater than GOES .
Several intervals are identified when the X-ray flux was exceptionally low , and the flux and solar X-ray luminosity are estimated .
Spectral fits to the emission at these times give temperatures of 1.7–1.9 MK and emission measures between 4 \times 10 ^ { 47 } cm ^ { -3 } and 1.1 \times 10 ^ { 48 } cm ^ { -3 } .
Comparing SphinX emission with that from the Hinode X-ray Telescope , we deduce that most of the emission is from general coronal structures rather than confined features like bright points .
For one of 27 intervals of exceptionally low activity identified in the SphinX data , the Sun ’ s X-ray luminosity in an energy range roughly extrapolated to that of ROSAT ( 0.1–2.4 keV ) was less than most nearby K and M dwarfs .